The present invention relates to a synchronized moving radiation shield apparatus including at least one shield block disposed under a radiation pathway of a radiation therapy unit used for radiation therapy for carcinomas in such a manner that a radiation field is formed with the shielding block, wherein an affected portion of a person is exposed to radiation through the radiation field while radiation therapy of a portion, other than the affected portion, of the person, is shielded by the shielding block. In particular, the present invention relates to a synchronized moving radiation shield apparatus configured such that radiation therapy of a portion, other than an affected portion, of a person is shielded by moving the radiation field in matching to the motion of the affected portion when the affected portion is subjected to radiation therapy.
A known radiation therapy unit used for radiation therapy for carcinomas or benign lesions is configured to have a lead block as a radiation shielding substance which is fixedly mounted to the unit in such a manner that a radiation field corresponding to an affected portion or a target is formed in the lead block, wherein the affected portion is subjected to radiation therapy through the radiation field and radiation therapy of a portion other than the affected portion is shielded by the lead block.
The above radiation therapy unit, however, has a problem. For example, for a patient having an affected portion in the lung, since the position of the affected portion is shifted by respiratory motion, adjacent normal portions of the affected portion should be exposed to radiation during radiation therapy of the affected portion. Accordingly, in consideration of radiation injury to adjacent normal portions of the patient, total radiation doses or daily fraction sizes must be limited, so that the affected portion may not be irradiated with sufficient doses.
An object of the present invention is to provide a synchronized moving radiation shield apparatus for shielding radiation therapy of a portion other than a moving affected portion of a patient to be exposed to radiation by moving a radiation field in accordance with the motion of the affected portion due to respiratory motion.
To achieve the above object, according to the present invention, there is provided a synchronized moving radiation shield apparatus including at least one shielding block disposed under a radiation pathway of a radiation therapy unit in such a manner that a radiation field is formed with the shielding block, wherein an affected portion of a person is exposed to radiation through the radiation field while radiation therapy of a portion, other than the affected portion, of the person, is shielded by the shielding block, the radiation shielding apparatus including: a movable portion for movably holding the shielding block while not blocking the passing of radiation through the radiation field; drive means, connected to the movable portion, for moving the radiation field to a specific position; and control means for controlling the drive means in such a manner that the radiation field is moving in matching to a variation in position of the affected portion.
With this configuration, it is possible to move the radiation field formed with the shielding block held by the movable portion in matching to the motion of an affected portion in which a lesion such as carcinoma necessary for radiation therapy has grown, that is, a target, by supplying a command corresponding to the motion of the affected portion to the drive means by the control means, and hence to prevent radiation therapy of a portion other than the affected portion even if the affected portion is moved in the body of a patient by respiratory motion upon radiation therapy for the patient.
Here, there may be adopted a configuration in which the motion of the affected portion is previously sampled and the sampled data is patterned, and the shielding block is moved in such a manner that the radiation field is moved on the basis of the patterned motion of the affected portion; however, according to the present invention, preferably, the control means controls the drive means in such a manner that the radiation field is located at a position corresponding to the affected portion while sequentially estimating the motion of the affected portion.
With this configuration, since the shielding block can be moved in such a manner that the radiation field is moved while following the motion of the affected portion, it is possible to more accurately perform the radiation therapy to only the affected portion. Preferably, the synchronized moving radiation shield apparatus further includes detecting means for sequentially detecting a variation in position of part of a body of the person correlated to the motion of the affected portion; wherein the control means comprises a microprocessor for automatically controlling the drive means on the basis of a detection value of the detecting means in accordance with a program for realizing alignment of the affected portion to he radiation field.
With this configuration, the microprocessor can effectively, instantly decide the movement direction and stoppage of the drive means in matching to a variation in position of the affected portion by sequentially measuring a change in oscillation of part of the body such as a chest wall varied depending on respiratory motion at significantly short intervals, that is, substantially continuously during radiation therapy by using a high resolution instrument such as a high speed measuring laser displacement gauge.
The movable portion preferably includes a base plate having a hole at a position matched to a movable range of the radiation field and fixed under the radiation therapy unit; rails provided on the upper surface of the base plate; and a movable plate having a hole at a position corresponding to the radiation field and movably disposed on the rails; wherein the shielding block is mounted on the movable plate in such a manner that the radiation field is formed with the shielding block, and the movable plate is moved on the rails by the drive means.
With this configuration, since the movable plate is moved along the rails by the drive means, it is possible to easily set the movement position of the shielding block and enhance the positional accuracy. In this case, since the movable plate has the hole at the position corresponding to the radiation field and also the base plate has the hole at the position matched to the movable range of the radiation field, the passing of the radiation through the radiation field is not obstructed.
Here, according to the present invention, in the case where the movable portion is configured such that the movable plate is movable along the rails as described above, if one set of the drive means and the movable plate on the rails are prepared, the shielding block can be horizontally moved along the longitudinal direction or X-direction; and if two sets of the movable plates on the rails and the drive means are prepared in such a manner that the base plate of the first movable portion is fixed to the radiation therapy unit, the base plate of the second base portion is mounted on the movable plate of the first movable portion with the rails of the first and second movable portions disposed in perpendicular to each other, and the shielding block is mounted on the movable plate of the second movable portion, the shielding block can be horizontally moved in the longitudinal and lateral directions or XY-directions. In the case of moving the shielding block in the XY-directions, the movable plate of the first or lower movable portion may be integrated with the base plate of the second or upper movable portion. Similarly, the shielding block can be configured to be movable in the three-dimensional directions or XYZ-directions.
The drive means is preferably composed of a stepping motor revolving on the basis of a pulse signal fed from the control means.
With this configuration, since the stepping motor or pulse motor accurately revolves and stops on the basis of a pulse signal fed from the control means with occurrence of little runout, the radiation field can be accurately moved in matching to the motion of the affected portion. To be more specific, even if a signal corresponding to a variation in the affected portion is continuously inputted in the microprocessor at very short intervals and is instantly converted into a pulse signal outputted as a command to the stepping motor, the motor can be accurately moved on the basis of the command with little runout. As a result, it is possible to accurately move the movable portion substantially in accordance with the motion of the affected portion.
The synchronized moving radiation shield apparatus preferably further includes detecting means for detecting the fact that the movable means is moved up to a critical position of the movable range.
With this configuration, even if there occurs any trouble, it is possible to prevent over-run of the movable portion.